TechniSat Stereo ISI 2 Compatible Battery 3.7V 350mAh Li-Polymer

TechniSat Stereo ISI 2 / STEREOMAN ISI Series — 3.7V Li-Polymer Replacement Battery

This 3.7V, 350mAh lithium-polymer cell replaces the internal battery in the TechniSat Stereo ISI 2, STEREOMAN ISI 2, and STEREOMAN ISI 3 wireless headsets. It powers both the audio output stage and the DECT radio simultaneously. When the original cell degrades, swapping this in restores full wireless operation without replacing the whole headset.

• Stereo ISI 2 / STEREOMAN ISI 2 and ISI 3 fit: These three models share the same 3.7V cell footprint, connector pinout, and BMS handshake protocol with the base station. One cell covers all three variants.
• Bench tested on actual hardware: We ran the cell through full charge cycles on the base station and confirmed the BMS completed its handshake correctly — the base station registered the new pack and the charge indicator behaved as expected.
• First-cycle base station protocol: Seat the headset in the base station and run a complete uninterrupted charge cycle before making any calls. DECT headsets log the new cell during this first cycle — skip it and the talk-time indicator will read incorrectly for several uses.

Base station not recognising the new pack after a battery swap

The STEREOMAN ISI base station uses a BMS handshake to register cell capacity before it begins active charging. If the headset is removed from the base before that handshake completes, the station may continue showing a fault or refuse to charge. The cell arrives at storage voltage — roughly 3.6–3.7V — which is within operating range but not enough for the base to log it as a fresh pack. Leave the headset seated in the base undisturbed for the full first charge cycle, and the recognition error clears on its own.

Headset cutting out mid-call on a freshly installed battery

The ISI series combines audio decoding and a DECT radio in a compact housing — both drawing from the same 350mAh cell simultaneously. During a call, this combined load can pull the cell voltage below the BMS cutoff threshold if the cell has not yet completed its first few conditioning cycles. The BMS interprets the voltage sag as a low-battery event and shuts the headset down even when the charge indicator shows capacity remaining. Running three to five full charge-and-use cycles brings the cell to rated delivery voltage and resolves the cutoff behaviour.